Dunnett Method

mice example

Setup

Assume data are in C2 (score) and groupings in C1 (group). Do StatANOVAGeneral Linear Model.

(mice01.png here)
Then click Comparisons
(mice02.png here)
and click Factor Plots
(mice03.png here)

Session Output

General Linear Model: score versus group 

Factor  Type   Levels  Values
group   fixed       3  1, 2, C


Analysis of Variance for score, using Adjusted SS for Tests

                                                 
Source  DF   Seq SS   Adj SS  Adj MS     F      P
group    2   673.00   673.00  336.50  4.55  0.029
Error   15  1109.50  1109.50   73.97             
Total   17  1782.50                              


S = 8.60039   R-Sq = 37.76%   R-Sq(adj) = 29.46%


Unusual Observations for score

Obs    score      Fit  SE Fit  Residual  St Resid
  2  32.0000  52.8333  3.5111  -20.8333     -2.65 R

R denotes an observation with a large standardized residual.


Bonferroni 95.0% Simultaneous Confidence Intervals
Response Variable score
Comparisons with Control Level
group = C  subtracted from:
                                |
group   Lower  Center  Upper  --+---------+---------+---------+----
1       2.137   14.50  26.86    |  (--------------*---------------)
2      -1.863   10.50  22.86  (-+------------*---------------)
                              --+---------+---------+---------+----
                              0.0       8.0      16.0      24.0


Bonferroni Simultaneous Tests
Response Variable score
Comparisons with Control Level
group = C  subtracted from:

                                                
       Difference       SE of           Adjusted
group    of Means  Difference  T-Value   P-Value
1           14.50       4.965    2.920    0.0211 *
2           10.50       4.965    2.115    0.1032


Dunnett 95.0% Simultaneous Confidence Intervals
Response Variable score
Comparisons with Control Level
group = C  subtracted from:
                                |
group   Lower  Center  Upper  --+---------+---------+---------+----
1       2.388   14.50  26.61    |  (--------------*--------------)
2      -1.612   10.50  22.61  (-+------------*--------------)
                              --+---------+---------+---------+----
                              0.0       8.0      16.0      24.0


Dunnett Simultaneous Tests
Response Variable score
Comparisons with Control Level
group = C  subtracted from:

                                                
       Difference       SE of           Adjusted
group    of Means  Difference  T-Value   P-Value
1           14.50       4.965    2.920    0.0195 *
2           10.50       4.965    2.115    0.0916

 

Both methods consistently imply that group 1 mean differs from the control group mean while group 2 mean does not.

The Dunnett's intervals are tighter than the respective Bonferroni's counterparts.

Main Effect Plot -- mice example

(mice04.png here)
Group 1 mean differs apparently from control group mean. It's less certain from the graph whether group 2 mean differs from control group mean.